This invention relates generally to tuning of frequencies, and particularly to adaptively extending a tunable range of frequency of a closed loop within a semiconductor device or a circuit.
To optimally operate a semiconductor device or a circuit, tuning of frequencies may be desired in a variety of situations. Extending a tunable range of frequency up to a full range of an oscillator is typically required in a closed loop system, such as a phase-locked loop or frequency synthesizer, as few examples. Although any one of different types of oscillators may be used in such a closed loop system, certain circumstances may limit the use to one type of an oscillator. For instance, stringent phase-noise specifications in most wireless standards dictate use of a LC oscillator, a resonant circuit containing inductors and capacitors. But LC oscillators can typically be tuned only over a relatively narrow range of frequencies, failing to cover the entire spectrum used by a particular wireless standard. When a tunable range is restricted only to the linear region of the frequency relative to the oscillator control voltage curve, the entire usable spectrum of a wireless standard may not be completely used. Wireless standards may mandate that semiconductor devices or circuits with a closed loop stay usable across multiple frequency bands.
For semiconductor devices or circuits fabricated using digital manufacturing processes, providing high-performance, low cost and power radio frequency (RF) transceivers pose additional challenges, especially in a single supply operation. Maintaining a settling time and phase noise performance at an adequate level may become difficult, in one case, since the transfer characteristic of such a device or a circuit becomes extremely non-linear at extreme ends. Even worse, power dissipation may increase at all frequencies because without incurring some penalty in power dissipation, an analog variable gain control may not allow a linear compensation of tuning characteristics of any general oscillator circuit.
Thus, there is a continuing need for better ways to controllably extend a tunable range of frequency in a closed loop, especially within a semiconductor device or a circuit.